Method of reusing slurry

ABSTRACT

A method of reusing a slurry in a ground improving method, wherein a hardening agent is injected into the ground, and wherein the muddy water (i.e., the slurry which is discharged) upon working is regenerated and again used as an injection material; namely, a hardening agent. By measuring the physical amount indicative of the permeability characteristic of the hardening agent contained in the slurry, an amount of hardening agent contained in the collected slurry (i.e., an amount of hardening agent to be collected) is calculated. Since the amount of collected hardening agent is calculated simultaneously with the collection of the slurry, the amount of hardening agent to be newly injected can be controlled in a real-time manner on the basis of the latest data (i.e., numerical value).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of reusing a slurry in a groundimproving method, wherein a hardening agent is injected into the ground,and wherein muddy water; i.e., slurry which is discharged upon workingthereof is regenerated and again used as an injection material; namely,a hardening agent.

2. Discussion of the Relevant Art

In the above-discussed method of reusing slurry, with respect to thehardening agent which is injected into the ground, the hardening agentof a quantity which is equal to or larger than the amount correspondingto the volume of a hole dug in the ground and gaps in the ground aredischarged as slurry onto the ground. The slurry which is dischargedonto the ground is at present abandoned as industrial waste. A dischargeamount of the slurry differs depending on the kind of the groundimproving method being employed. In addition, the content of sediment inthe discharged slurry also differs depending on the working conditionand working method being employed.

However, the process for abandoning the slurry as industrial wastecauses an increase in processing cost. In addition, a present situationwherein the decrease in the number of construction for processingfacilities of the industrial wastes facilitates an increase inprocessing cost. Therefore, there is a strong demand for reusing theslurry for the hardening agent contained in the slurry.

When reusing the slurry, a technique for measuring a quantity ofhardening agent contained in the discharged slurry is inevitable.Techniques for measuring an amount of hardening agent contained in theslurry includes a calcium analysis method, a pH measuring method and aboron tracer.

The calcium analysis method is a method whereby after an amount ofcalcium in a consolidation sample is measured, a calcium elementcomponent of the hardening agent is counted back and a content of thehardening agent is obtained from the calcium element component. However,the above method has a problem in that a fairly large amount of labor isexpended to measure the content.

The pH measuring method estimates a range of an amount of hardeningagent on the basis of the numerical value obtained from the workingprocesses (i.e., actual results) from an alkalinity (pH) which thehardening agent liquates and physical properties (i.e., specific gravityor the like) of the discharged slurry. However, according to thismethod, since the numerical values obtained from the actual results areused, there is a problem in that the latest information cannot beobtained on every ground.

The boron tracer method is a method whereby by using the principle inwhich boron atoms absorb the neutrons, boron atoms are mixed into thehardening agent so as to keep a concentration of boron atoms constant,the number of boron atoms is measured, and thereby, obtaining a quantityof hardening agent. This method has an advantage in that thequantitative measurement of the hardening agent can be performed.However, there is a problem in that a radioactive isotope (RI) must beused upon measurement.

The present invention is made in consideration of the problems of theconventional techniques mentioned above, and it is an object of thisinvention to provide a method for reusing a slurry in the ground,wherein a quantity of the hardening agent contained in a dischargedslurry can be accurately and suitably measured and the demand to reusethe slurry (i.e., the hardening agent contained in the slurry) can besatisfied.

SUMMARY OF THE INVENTION

This invention relates to a method of reusing a slurry in a groundimproving method, wherein a hardening agent is injected into the ground.The method comprises the steps of adding a material having apermeability into the hardening agent to be injected, measuring aphysical amount indicative of a permeability characteristic of thehardening agent added with the substance, and calculating an amount ofhardening agent from the physical amount. The method further includesthe steps of: collecting the slurry which is discharged upon executionof the ground improving method; measuring the physical amount in thecollected slurry and calculating an amount of collected hardening agent;and calculating a difference between an injection amount of thehardening agent which is needed to improve the ground and the collectedamount of hardening agent and injecting the hardening agent of theamount corresponding to the difference.

In this invention, it is preferable to use cement as a hardening agentand to use ferrite as a material having the permeability.

It is now assumed that a grain diameter of a cement particle is set tod_(a), a grain diameter of a ferrite particle is set to d_(b), aspecific gravity of a cement particle is set to δ_(a), a specificgravity of a ferrite particle is set to δ_(b), and a specific gravity ofthe suspension of cement and ferrite is set to δ_(s). It is nowpreferable to select the cement particles and the ferrite particles soas to conform to the following equation: ##EQU1## This is because cementand ferrite perform the same motion in the mixture and a distributionratio in the mixture is set at a constant value and the content of thecement in the slurry can be accurately calculated.

According to this invention, having the above-discussed construction, bycollecting the discharged slurry and measuring the physical amountindicative of the permeability characteristic of the hardening agentcontained in the slurry, an amount of hardening agent contained in thecollected slurry; i.e., an amount of hardening agent to be collected iscalculated. By comparing an amount of hardening agent which is needed toimprove the ground and has previously been known, and the amount ofcollected hardening agent and by obtaining the difference therebetween,the amount of hardening agent to be newly injected is calculated.

As mentioned above, according to this invention, since the amountcollected hardening agent is simultaneously calculated with thecollection of the slurry, the amount of hardening agent to be newlyinjected can be controlled in a real-time manner on the basis of thelatest data (i.e., numerical value). Thus, the slurry can be used againin a fully automated system.

In this invention, a material having the permeability is used as atracer and the material having the permeability is harmless for thehuman body as compared with a radioactive material or the like. Inaddition, since the hardening agent is used again, an amount ofhardening material to be processed as an industrial waste decreases.Therefore, according to the operation of this invention, the generationof public pollution can be also suppressed.

On the other hand, by properly selecting an additive material having thepermeability, the motions of the additive material and the hardeningagent can be made coincident so that the calculated amount of thecollected hardening agent also has an accurate numerical value.

These and other features of this invention will be understood uponreading of the following description along with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a procedure of an embodiment of thepresent invention;

FIG. 2 is an explanatory diagram of the measurement principle in thepresent in invention;

FIG. 3 is an explanatory diagram of a measuring apparatus which is usedin the present invention;

FIG. 4 is a characteristic graph showing permeabilities and contents ofcement which were measured by using the measuring apparatus of FIG. 3;

FIG. 5 is a diagram showing a table of the accuracies of the results ofthe measurements which were measured in accordance with the measurementswhich were measured in accordance with the measurement principle of thepresent invention; and

FIG. 6 is a diagram showing a table of the strengths of respectiveportions of the columnar consolidation bodies constructed in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an outline of an embodiment to which the invention isapplied in what is called a column jet grouting method. After ahardening agent 2 comprising water 1 and cement is measured by weighingapparatuses 3 and 4, respectively, it is injected into a mixer 5 andmixed and stirred. The stirred material of the water and hardening agentis transferred into a first reservoir stirring tank 6 and properlystirred. In this stirring state, the stirred material is held in a statesuitable for the ground improving work. Magnetic particles are uniformlymixed in the hardening agent 2.

When executing the ground improving work, the stirred material of thewater and hardening agent is first fed into a second reservoir stirringtank 8 by a force feed pump 7 and is subsequently sent to a groundimprovement working site 10 by an injection pump 9. In the groundimprovement working site 10, a hole is dug in the ground, the stirredmaterial of the water and hardening agent is spouted out into the hole,and a columnar consolidation body is formed.

The stirred material which is not used to construct the columnarconsolidation body is discharged as a discharge muddy water or slurry 11together with the sediment at the working site from the hole dug in theworking site. The slurry 11 is sent to a hardening agent collecting step(line L₁₂) by a sand pump 12. The coarse particle sediment contained inthe slurry which is sent through the line L₁₂ is separated by avibration sieve 13 and discharged so that the slurry is set into a statein which it can be used again (step S₁₂).

The slurry from which the coarse particle sediment is separated from andwhich can be used again is sent to a reservoir tank 14 and its densityis measured in the reservoir tank by a densitometer 15. The measureddensity is inputted to a computer 16 (line L₁₅). On the other hand, thereusable slurry is sent from the reservoir tank 14 into the secondreservoir stirring tank 8 through a flow meter 18 by a force feed pump17. At this time, a flow amount of the reusable slurry which wasmeasured by the flow meter 18 is inputted to the computer 16 (line L₁₈).An impedance as a physical amount indicative of the permeabilitycharacteristic of the hardening agent contained in the reusable slurryis measured by an impedance analyzer 19 and inputted to the computer 16(line L₁₉).

When the density, flow amount, and impedance of the reusable slurry areinputted to the computer 16, the computer calculates the amount ofhardening agent contained in the slurry; i.e., the amount of hardeningagent collected from those measured values. A difference between theamount of hardening agent which is needed for the ground improving workand the amount of collected hardening agent is calculated by thecomputer 16 and a control signal is transmitted from the computer 16 tothe force feed pump 7 so as to supply the hardening agent of the amountcorresponding to the calculated difference from the first reservoirstirring tank 6 (line L₁₆). Thus, the amount of collected hardeningagent is obtained in a real-time manner and the hardening agent of theamount which is necessary and enough for the ground improving work isaccurately supplied.

The principle in which the impedance exhibits the permeabilitycharacteristic of the hardening agent will now be described withreference to FIG. 2. FIG. 2 shows a state in which a magnetic material22 is inserted into a hollow coil 20.

An impedance Z₀ of the hollow coil 20 is given by the followingequation:

    Z.sub.0 =R.sub.0 +jωL.sub.0.

When it is assumed that an inductance is set to L₀, an internalresistance is set to R₀, and a pure imaginary number is set to j.

When a permeability of the magnetic material 22 assumes μ and themagnetic material 22 is inserted into the hollow coil 20, an impedanceZ₁ of the coil is given by the following equations:

    Z.sub.1 =R.sub.0 +ωL.sub.0 (S.sub.1 /S.sub.0)μ.sub.B +{jωL.sub.0 (S.sub.0 -S.sub.1 +μ.sub.A S.sub.1)/S.sub.0 }

where, μ_(A) A is a real number part of the permeability μ and μ_(B) isan imaginary number part of the permeability μ. That is, thepermeability μ is expressed by the equation:

    μ=μ.sub.A -Jμ.sub.B

On the other hand, the impedance Z₁ of the coil when the magneticmaterial 22 is inserted into the hollow coil 20 is expressed by theequation:

    Z.sub.1 =R.sub.1 +jωL.sub.1.

    Therefore,

    R.sub.1 =R.sub.0 +ωL.sub.0 (S.sub.1 /S.sub.0)μ.sub.B ; and

    L.sub.1 =L.sub.0 (S.sub.0 -S.sub.1 +μ S.sub.1)/S.sub.O.

By deriving μ_(A) and μ_(B) from the above two equations, respectively,

    μ.sub.A =(S.sub.0 /S.sub.1){(L.sub.1 /L.sub.0)-}+1; and

    μ.sub.B =(S.sub.0 /S.sub.1){(R.sub.1 -R.sub.0)/ωL.sub.0 }.

Therefore, the permeability μ of the magnetic material 22 can beobtained if the impedance Z₁ and a resistance of the coil in the hollowstate in which the magnetic material 22 is not inserted and an impedanceZ_(O) and a resistance of the coil in a state in which the magneticmaterial 22 is inserted are known. In this case, if a substancecomprising a material having no magnetic loss until a high frequencyrange is used as a magnetic material 22, μ_(B) =0 and only μA exists atthe measuring frequency. Therefore, if a change in inductance of thecoil is known, the permeability μ of the magnetic material 22 isobtained.

In the case where the magnetic particles are mixed and distributed intoa non-magnetic material, the permeability of the mixture changesdepending on a concentration of magnetic material. If the permeabilityof the mixture is known, an amount of magnetic material can be known. Inthis invention, since the magnetic material is uniformly mixed intohardening agent at a predetermined ratio, the amount of magneticmaterial is proportional to the amount of hardening agent. Therefore,the amount of hardening agent can be obtained if the amount of magneticmaterial is known from the permeability of the mixture.

FIG. 3 shows an example of an apparatus for measuring a permeability inthe invention. In FIG. 3, a coil 28 is formed by winding a coveredcopper wire 26 around a glass tube 24 and the collected slurry (notshown in FIG. 3) is allowed to flow in the glass tube 24. An inductanceof the coil 28 is measured by an impedance analyzer 30. The permeabilityof the slurry flowing in the glass tube 24 can be obtained on the basisof the foregoing principle.

FIG. 4 shows the results of the measurements in the detection of theconcentration of ferrite cement in the case where a mixture of the waterand ferrite cement which is obtained by mixing the ferrite particleshaving an average grain diameter of 2.5 μm into 5 weight % of cement (anaverage grain diameter being 15 μm) is allowed to flow into the glasstube 24 in place of the slurry and the concentration of ferrite cementis variously changed. As will be understood from FIG. 4, thepermeability changes in proportion to the concentration of the ferritecement, and if the permeability is known, the concentration (namely, thecontent of ferrite cement) is obtained.

In order to obtain the content of the hardening agent (i.e., the ferritecement) from the permeability, it is necessary that the magneticparticles as a tracer are uniformly mixed into the hardening agent as anon-magnetic material and that when the hardening agent is diluted bythe water or the like, the magnetic material and the hardening agentperform the same motion. In other words, in the case where the magneticparticles precipitate in the hardening agent or the magnetic particlesare separated from the hardening agent, the proportional relationbetween the permeability and the content of the hardening agent is notsatisfied and the invention cannot be embodied. The conditions in whichthe magnetic particle and the hardening agent perform the same motionwill now be described hereinbelow. It is now assumed that cement is usedas a hardening agent and ferrite is used as a magnetic particle.

In the interference drop in which a number of particles drop whileexerting influences on each other in the suspension, and in a rangewhere Stokes' law is satisfied, a drop velocity V_(s) of the particle isgiven by the following equation:

    V.sub.S ={(δ-δ.sub.s)d.sup.2 }/(18n.sub.s),

where δ is a specific gravity of the particle, δ₂ is a specific gravityof suspension, d is a diameter of particle, and δ_(s) denotes aviscosity of suspension.

For instance, in the particles (such as, cement and ferrite) havingspecific gravities which differ, the particles having the equal dropvelocity are called uniform speed drop particles and a ratio of sizes ofthe uniform velocity drop particles is called a uniform velocity dropratio. The uniform velocity drop ratio is given by the followingequation: ##EQU2## where d_(a) and d_(b) denote diameters of two kindsof particles and δ_(a) and δ_(b) indicate specific gravities of twokinds of particles.

By selecting cement and ferrite which satisfy the condition which isgiven by the above equation, both cement and ferrite perform the samemotion in the suspension; i.e., mixture fluid. However, since there is avariation in grain diameters of the actual particles, to meet thecondition of the above equation, it is preferable that the graindiameter of the particle having a larger specific gravity is set to besmaller than the numerical value which is obtained from the aboveequation.

Explanation will now be provided with respect to the comparison ofmeasurements in the case where ferrite cement of 5 weight % is used as ahardening agent mixed with the magnetic particles and the permeabilityof the discharged slime having been obtained, and the amount ofcollected cement being measured due to the embodiment shown in FIG. 1and the results of the measurements in the case where a CaO quantityhaving been obtained by the chemical analysis and the amount ofcollected cement being measured from the CaO quantity. The testconditions are set as follows. A ferrite concentration is set to 5weight %. An average grain diameter of ferrite is set to 2.4 μm. Alength (column length) of columnar consolidation body which is formed bythe ground improving work is set to 4 m. An injection agentconcentration (W/C) is set to 100%. A nozzle pull-up velocity in theground improving work is set to 5 cm/min.

As can be understood from FIG. 5, the results of the measurements of theamount of cement, according to the embodiment shown in FIG. 1, exhibitsonly an error of about 10% as compared with the results of themeasurements by the chemical analysis. Therefore, it will be understoodthat when the invention is embodied, the amount of collected cement isaccurately calculated.

FIG. 6 shows the results of the strength tests of the columnarconsolidation bodies constructed by using the slurry (i.e., hardeningagent contained therein) which is reused according to this invention.

As can be seen from the results of the strength tests, it will beunderstood that the columnar consolidation bodies constructed by theabove-described embodiments of this invention have the uniform strengthand extremely good strength characteristics.

As described above, according to this invention, an amount of hardeningagent contained in the discharged slurry is accurately calculated in areal-time manner and the difference between the amount of hardeningagent which is needed for the ground improving work and the amount ofcollected hardening agent is soon obtained. Therefore, the hardeningagent is effectively used and an amount of hardening agent to beabandoned is remarkably reduced. Further, the reuse of slurry or thereuse of cement contained in the slurry can be performed in a fullyautomated system.

On the other hand, since the magnetic particles have been used as atracer, the tracer does not exert an adverse influence on the human bodyand does not become a cause of public pollution.

Further, the columnar consolidation body constructed by the embodimentsof this invention has a uniform strength as a whole and has goodstrength characteristics.

While the invention has been particularly shown and described inreference to preferred embodiments thereof, it will be understood bythose skilled in the art that changes in form and details may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method of reusing a slurry in a groundimproving method whereby a hardening agent is injected into the ground,comprising the steps of:adding a substance having a permeability intosaid hardening agent to be injected; measuring a physical amountindicative of a permeability characteristic of said hardening agentadded with said substance; calculating a quantity of the hardening agentfrom said physical amount; collecting said slurry which is dischargedupon execution of the ground improving method; measuring the physicalamount in said collected slurry and calculating a quantity of saidcollected hardening agent; and calculating a difference between aninjection amount of said hardening agent which is needed to improve theground and the quantity of said collected hardening agent and injectingsaid hardening agent with an amount corresponding to the difference.